1. Field of the Invention
The present invention relates to a developer for developing electrostatic latent images, and in particular, to a developer for developing electrostatic latent images used in electrophotography, electrostatic printing or the like. The developer includes so-called "toner". Further, the toner may be used together with a carrier such as solid particles, for example, iron powder, and glass beads, and insulating liquids.
The present invention more particularly relates to a developer for color electrophotography where a plurality of color toners including magenta, cyan and yellow toners or for electrophotographic printing process where letters, patterns and the like are printed on cloths by using electrophotography. 2. Description of the Prior Art
There are known photographic methods or printing methods comprising forming electrostatic latent images on a surface of an image forming member such as a photosensitive member composed of a photoconductive material, and visualizing the electrostatic latent images with toner. For example, such electrophotographic methods are disclosed in U.S. Pat. No. 2,297,691, Japanese Patent Publication Nos. Sho 42-23910, Sho 43-24748 and the like. These methods usually comprise using a photoconductive material as a photosensitive material, charging, exposing, other procedures to produce electrostatic latent images on the photosensitive material, if desired, transferring the resulting toner images onto a receiving member, or transferring the electrostatic latent images to a receiving member followed by developing with toner, and then fixing with heat, pressure or a solvent vapor, to obtain a copy. As a method for visualizing electrostatic latent images with toner, there are known various methods, for example, a magnetic brush method as disclosed in U.S. Pat. No. 2,874,063, a cascade method as in U.S. Pat. No. 2,618,552 and a powder cloud method as in U.S. Pat. No. 2,221,776. As toners used in these developing methods, there are known fine powders composed of dye or pigment dispersed in a binder, and toners containing various additives as disclosed in Japanese Patent Publication Nos. Sho 38-11096, Sho 40-10866, and Sho 44-6398.
The above mentioned developing methods are called "dry developing process". In the dry developing process there may be used iron powder, glass beads as a carrier together with a toner, or there may be not used any carrier. Further, there are known wet developing methods, where a toner is dispersed in a highly insulating solvent such as Isopar H (trade name).
Further there is known a color electrophotographic process where color reproduction of a color original is conducted by electrophotography. This process is carried out by exposing a panchromatic photosensitive member subsequently through color separation filters of blue, green and red to produce the corresponding electrostatic images, developing with yellow, magenta, and cyan toners subsequently, overlying the developed images or transferring the developed images subsequently to a receiving sheet, and then fixing to produce a colored copy. Further, if desired, a black toner is used for emphasizing image shadow portions.
In a color electrophotographic process containing the above mentioned color image forming steps it is not easy to obtain stable images constantly owing to change of charging properties of each color toner with the lapse of time. In addition, in color electrophotographic processes it is sometimes necessary to change optionally the degree of color mixing in accordance with user's taste. Therefore, color electrophotography is subjected to various limitations as to the developer, in particular, composition of toner as compared with monochromic electrophotography. There have been recently developed electrophotographic printing process for printing patterns on cloth or textile. Such electrophotographic printing process may be effected by forming electrostatic latent images corresponding to desired patterns and letters, developing the latent images with a toner for electrophotographic printing, transferring the developed images to cloths, steaming, soaping and drying. The formation of the electrostatic latent images may be conducted by one of various electrophotographic processes such as Carlson process as disclosed in U.S. Pat. No. 2,297,691, Electrofax process described in C. J. Young, H. G. Greig et al.: RCA Rev. 15, 469 (1954), Canon NP process as disclosed in U.S. Pat. Nos. 3,666,363 and 3,438,706.
The printing toner used for the electrophotographic printing process is required to dye chemically various cloths, give sharp patterns, and have wash resistance, heat resistance when ironed, and sun light resistance. Therefore, conventional electrophotographic toners to be transferred to papers and attached physically or electrically can not be simply used for the electrophotographic printing on cloths.
According to electrophotographic printing processes, after transferring printing toners, the toners are subjected to steaming, soaping, and drying so as to dye cloths with a dyestuff contained in the toner, and if necessary, a resin constituting a toner is removed. Therefore, the toner for electrophotographic printing processes is different from toners to be transferred to or fixed to papers with respect to the composition.
As printing toners, there are usually used natural or synthetic vehicle resin and a water soluble dye. The dye varies depending upon the type of cloth material. For example, a disperse dye is used for polyester fiber, a cation dye for acrylic fiber, an acid dye for polyamide fiber and wool, and reactive dye, direct cotton dye, sulfur dye for cellose and silk fiber.
As mentioned above, the dye used for printing toners varies depending upon type of cloth and color. Consequently it is difficult to control chargeability of printing toner using various dyes. In addition, many colors should be prepared to meet user's taste. This can be done by preparing some elemental color toners and mixing them accordingly to obtain desired color. However, it is difficult to uniformly control the chargeability of such mixed toner.